This invention relates to passive optical elements and, more particularly, to passive optical collimating elements.
When laser or LED light is emitted from lasers (or output from fibers to detectors or modulators), the light diffracts (i.e. it spreads out as it travels). If that light is allowed to traverse a large distance without entering a fiber or being focused by a lens, it spreads out in area quickly. If the optical devices which emit or receive this light are spaced close to one another in an array light from/to one optical device can mix with the light to/from adjacent devices.
FIG. 1 shows such a condition where light is output from an array of lasers and the light from each one spreads out. If the distance the light travels in free space is long enough (typically on the order of 50 micrometers based upon a typical laser-to-laser spacing (i.e. the xe2x80x9cpitchxe2x80x9d) of 125 to 250 microns, the light will spread out enough before it reaches its destination fiber such that it will mix with the light from at least other adjacent devices. This is called crosstalk and it degrades the data integrity coming from each of the devices or going into the fibers.
It is well known that crosstalk is undesirable. One option for eliminating crosstalk is to ensure that the fibers from a fiber cable are placed close enough to the lasers (or detectors) so that the light reaches its destination (i.e. the fiber or device) before it spreads out too much.
Some optical module companies have relied on this approach. Unfortunately, most users of components want optical components with removable cables; having to xe2x80x98snapxe2x80x99 in and out.
Unfortunately, a cable where the fibers come extremely close to the optical devices provides great potential for damage the individual devices caused by impact of an end of a fiber with a device. In addition, when a fiber cable is removed, the individual optical devices are exposed to ambient environmental conditions, including humidity, which can adversely affect the lifetime of the devices.
Optical transceiver groups have been looking at 1-D arrays of optical devices (rather than 2-D) and have typically tried to have the optical fibers themselves inserted so the attach very close to the devices. The resulting yield, reliability and failure of the devices have limited the usefulness of this technique.
Others have made 1-D devices where they use a series of independent separate fibers and attach them to a piece of silicon and then attach the silicon to piece to a module board on which the optical devices reside. Such pieces however, are not compatible with commercial connectors.
Still others have made 2-D arrays of optical devices for use in digital video cameras (CCD cameras). These products use what is called a fiberoptic faceplate which is a fused fiber bundle where the number of fibers far exceeds the number of optical devices, particularly on a use basis. These faceplates are attached to a mounting layer right on the electronic chip itself. With a faceplate, there is no alignment required between the optical devices and the faceplate itself since there are many more fibers than optical devices, the light to/from the optical devices will pass through at least several fibers regardless of alignment. One such example is shown in U.S. Pat. No. 5,074,683.
However, the approach of U.S. Pat. No. 5,074,683, where a piece is directly attached to the optical chip, forces one to construct structures on the optical chip onto which a coupler could be placed. The height of such structures would be a pre-determined height and could face tolerance errors which would limit the accuracy of height placement.
In addition, when coupling light into fiberoptic faceplates, because there are many more fibers than devices, some of the light can go into a variety of fibers and other portions of the light will miss all of the fibers and be lost. In addition, spot spreading occurs in fiberoptic faceplates which limits the efficiency of coupling.
Thus, what is needed is a way to couple light to a fiber that eliminates crosstalk.
What is also needed is a way to encapsulate optical devices to avoid exposure to ambient conditions.
What is further needed is a way to protect the surface of the devices from being impacted by fibers in a connector when it is inserted and/or removed.
In general, we have devised a way to overcome the problems noted above through the use of a fused glass fiber array integrated into an opto-electronic module.
We have also created an assembly methodology for integrating the optical coupler with optical device/electronic chip pieces. The integration methodology is broadly applicable to optical couplers made via other technologies.
One aspect of the invention involves an optical unit. The optical unit has multiple optical devices, a collimated coupler disposed relative to the multiple optical devices so that laser light can be transferred between at least two of the multiple optical devices and the collimated coupler without crosstalk, and a fused glass collimator, disposed within the collimated coupler, having multiple optical fibers arranged in a predetermined arrangement relative to the multiple optical devices so that the number of optical fibers is always equal to or greater than the number of optical devices on a use basis.
The advantages and features described herein are a few of the many advantages and features available from representative embodiments and are presented only to assist in understanding the invention. It should be understood that they are not to be considered limitations on the invention as defined by the claims, or limitations on equivalents to the claims. For instance, some of these advantages are mutually contradictory, in that they cannot be simultaneously present in a single embodiment. Similarly, some advantages are applicable to one aspect of the invention, and inapplicable to others. Thus, this summary of features and advantages should not be considered dispositive in determining equivalence. Additional features and advantages of the invention will become apparent in the following description, from the drawings, and from the claims.